The present invention relates to an electronic control unit containing an electronic device and preferably applied to engine control units (ECUs) for engines.
An electronic control unit suitable for use in the ECUs has a printed circuit board where a plurality of electronic devices, such as a microcomputer, are mounted. The electronic control unit also has a case in which the printed circuit board is contained.
A conventional electronic control unit is illustrated in FIG. 12. In FIG. 12, a connector J2 is attached to one side wall J1a of a case J1 for containing the printed circuit board.
That is, the case J1 is formed at its one side wall J1a with a concave groove J3 having a substantially trapezoidal shape. The connector J2 is fixedly fitted in the concave groove J2 through a seal member J4. The seal member J4 is disposed between an outer peripheral portion of the connector J2 and an inner peripheral portion of the concave groove J3 to be closely adhered on them. This gives a waterproof connection between the connector J2 and the case J1.
The outer peripheral portion of the connector J2 includes a lateral surface J7 and a longitudinal surface J8. The longitudinal length of the longitudinal surface J8 is longer than that of the lateral surface J7. The first and longitudinal surfaces J7 and J8 are parallel to each other.
The outer peripheral portion also includes an inclined side surface J5 connecting one end of the lateral surface J7 and one end of the longitudinal surface J8, and an inclined side surface J6 connecting the other end of the lateral surface J7 and other end of the longitudinal surface J8. The inclined side surfaces J5 and J6 are not paralleled to each other.
The inner peripheral portion of the concave groove J3 includes a base surface J9 opposed to the lateral surface J7. The inner peripheral portion of the concave groove J3 also includes an inclined side surface J10 connected at its one end portion to one end of the base surface J9 and opposite to the inclined side surface J5. The inner peripheral portion of the concave groove J3 also has an inclined side surface J11 connected at its one end portion to the other end of the base surface J9 and opposite to the inclined side surface J6.
The connector inclined angle X between the lateral surface J7 and the inclined side surface J5 and that between the lateral surface J7 and the inclined side surface J6 are equal to each other. Similarly, the case inclined angle Y between the bottom surface J9 and the inclined side surface J10 and that between the bottom surface J9 and the inclined side surface J11 are equal to each other. In addition, the connector inclined angle X and the case inclined angle Y are also equal to each other.
In the structure of the electronic control unit, if the connector J2 thermally expands, as shown in FIG. 13, the dimensional change of the longitudinal surface J8 is larger than that of the lateral surface J7. This causes the seal member J4 in part of its longitudinal surface J8 side to be highly compressed so that a crack may occur in the seal member J4.
If the crack occurs in the seal member J4 between the connector J2 and the case J1, it might be difficult to maintain the airtightness environment of the electronic control unit.
This problem may become much more prominent when the connector J2 is made of a material with a first linear expansion coefficient and the case J1 is made of another material with a second linear expansion coefficient that is different from the first liner expansion coefficient.
In addition, if the case inclined angles are shapely inclined, when fitting the connector J2 into the inner peripheral portion of the concave groove J3, on which the seal member J4 is previously adhered, the connector J2 may press the seal member J4 in part of its longitudinal surface J8 side into the base surface J9 side of the case J1 (low side in FIG. 14A).
If the part of seal member J4 in its longitudinal surface J8 side is pressed into the base surface J9 side of the case J1, the fill quantity of the seal member J4 may be insufficient at the gaps G between the longitudinal side portion of the connector J2 and each other end portion of each of the inclined side surfaces J10 and J11 (see FIG. 14B).
The full quantity of seam member J4 may be inadequate in maintaining the airtightness of the electronic control unit between the connector J2 and the case J1.